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[TASS] MKIV Darks and Flats
On Thu, 16 Dec 1999 17:57:37 -0500, Glenn Gombert
> I am most curious what Andrew did to solve this problem (using custom made
>dark/flat frames) it looks like.
1) "Dark" is point-by point median of 2032x2032 image area for the 3
dark images for each camera on CD5. Not great, being median of
just 3 values per point, but it does catch enough of the hot
points to save Star from getting bamboozled. The first version
has no allowance for variation of the mean or scaling between images.
I intended to write a program to use a catalog of hot
locations and to replace every hot point with a median of
adjacent points. This program got put on hold when the simple
subtraction "worked" but I think this is the right way to go.
There are just too many intermittent hot pixels not to do
2) "Flat" is a point by point median of the 35 image areas. Each
point is dark-subtracted and scaled by 32768/(image median -
dark median). This is pretty rough too; I didn't purge the
cloudy images first. Or the airplanes. Or those fascinating
bands, whatever they are that don't look like clouds or airplanes.
Applying these with my Borland Pascal 7.0 program, again without
any allowance for Dark scaling, reduced the noise level reported
by Star by almost a factor of 2. I keep meaning to try Dark and
Flat separately to see which does most for the noise but have not
got round to it.
3) At least as important as Dark/Flat for getting Star to work
properly in catalog matching is getting rid of the "saturated"
I apologise that the programs are written in Borland Pascal 7.0.
This is a most unsuitable language with lots of remaining 16-bit
restrictions but I am fluent in it, unlike C, which I read with
difficulty and as yet don't write at all. C is my Millennial Project.
At Glen Gombert's request, I am posting some of the code on my
website (original .PAS files as .txt); links are at the bottom of
the revised version of my preliminary "saturated" star analysis at:
Andrew Bennett, Avondale Vineyard, Nova Scotia, Canada.